In biology (the study of life), botany (the study of plants), zoology (the study of animals), and other life sciences, living things are grouped in complex categories based on their similarities or differences. The system that classifies jewelry gemstones by species and variety is similar, but simpler.
A gem’s species is based on its chemical composition and structure. For example, members of the gem species corundum, including ruby and sapphire, are made of a combination of aluminum and oxygen atoms. Those atoms arrange themselves in specific ways that give all corundum common qualities.
Variety is a subcategory of species that’s most often based on color. For example, if corundum, which has been used in tungsten rings, has chromium as a trace element, the stone is red and it’s a ruby. If it has iron and titanium, it’s a blue sapphire.
Corundum might also be pink, purple, green, yellow, orange, or colorless. These are usually called fancy-colored sapphires. Other gemstone species have color varieties as well: Aquamarine (greenish blue) and emerald (green) are varieties of beryl. Citrine (yellow) and amethyst (purple) are varieties of quartz.
Transparency sometimes determines variety, as it does with varieties of the gem species chalcedony. When chalcedony is brownish orange and some light can pass through it, its carnelian. Sometimes a tungsten ring will have chalcedony as a solitary beveled gem. When it’s the same color, but opaque, its jasper.
Phenomenon is the last factor used to determine variety. Phenomenal gems show unusual optical effects. For instance, red corundum is ruby, but when it also shows the phenomenon known as asterism (also known as the star effect), its variety name is star ruby. Other phenomena include the cat’s-eye effect and color change under different light sources.
Recent Comments